Shawn Motors in Costa Mesa (250 briggs ave.)
This is a little known shop and i've gone through hell and back with them rebuilding my car from totaled (pulled engine and a rebuilt frame rail) to 100% functional but I trust them with my 3er. Pretty reasonable pricing if you know how to talk shop with them and haggle too.

Hey guys..I just got my jb4 G5 ISO in th email along with my VRSF downpipes from Mike@n54tuning and I need a shop that would be able to install these bad boys. Didnt really feel like reading all the posts so any suggestions would be amazing. Oh, and by the way, I live in SD so anywhere nearby would be great! Thanks!!!

Hey guys..I just got my jb4 G5 ISO in th email along with my VRSF downpipes from Mike@n54tuning and I need a shop that would be able to install these bad boys. Didnt really feel like reading all the posts so any suggestions would be amazing. Oh, and by the way, I live in SD so anywhere nearby would be great! Thanks!!!

i have a friend that opened his own shop and mainly works on BMWs only, let me ask him for you

They perform all factory repairs. They are a Dinan authorized dealer, factory tools and equipment. Family owned business. Great place for all your german car needs.
I've had them do all my coding and installed my supercharger, brembo brakes, and many other services. Great shop !
Ask for Erik and reference this forum, he will get you a discount.